Pertaining to a margin; situated on or near the margin; specifically, written or printed in the margin of a page: as, a marginal note or gloss.n. One of the bones which form the border of the carapace in turtles, except in the Trionychoidea, in which they are lacking: same as marginal plate. See cut under carapace, 1.n. In the ammonoid cephalopods, or ammonites, one of the small inflections which sometimes develop on the sides of the antisiphonal lobe of the sutures.n. In conchology, one of the outermost teeth on the radula of gastropods; one of the uncini.n. In asteroid echinoderms, one of the series of thick plates round the margin of the arms and disk.